[postgis-users] Performance comparison between PostGIS's topology creation and topojson (the module)

[Rémi Cura]

Hey,
Sandro could you give more details about how postgis topology use
PolygonizeGraph in GEOS?

In particular, is there a geos graph corresponding to a topology or is it
rebuild every time we need to make a change to this graph? (is only a small
part rebuild or the whole graph?)
If it is stored, is it in cache or serialized and put in db?

And how does it work when inserting/deleting/changing a line into the
topology model regarding this geos topological graph?

Thanks,
Rémi-C





2014-03-18 8:36 GMT+01:00 Sandro Santilli <strk at keybit.net>:

> On Tue, Mar 18, 2014 at 11:04:27AM +1100, Luca Morandini wrote:
> > On 18/03/14 10:28, Stephen V. Mather wrote:
> > >I don't know.  Javascript is pretty fast these days. Given this and 1)
> no
> > >database overhead, 2) Not the same level of completeness to the
> algorithm, I
> > >would not be surprised by the JS being faster, in fact I'd expect it.
> >
> > Certainly transactions are an overhead, but closeness to the data
> > should be an advantage (though not that large for small datasets).
>
> You fetch all the data into memory before turning into TopoJSON,
> so the data is immediately available also to javascript.
>
> > Actually, I presume adding one geometry at a time may be the real
> > performance killer, compared with knowing in advance all the
> > geometries that make the topology.
>
> That's the other aspect of it, but as I said the PostGIS equivalent
> of that (CreateTopogeo) is currently also not optimized to take
> advantage of that. I'd love to see some contribution in the direction
> of speeding that up :)
>
> --strk;
>
>  ()  ASCII ribbon campaign  --  Keep it simple !
>  /\  http://strk.keybit.net/rants/ascii_mails.txt
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